The present invention relates to a welding sleeve made of a thermoplastic, the inside of which is provided, at least locally, with electrically conductive materials embedded in the wall and with at least two connecting means embedded in the sleeve wall for connecting the said electrically conductive material to an external voltage source, said connecting means extending maximally to the inner wall of the welding sleeve.
A welding sleeve of this type is generally known. For connecting tubes made of a thermoplastic with one another, the extremities of these tube parts are pushed into the welding sleeve, and this is followed by application of an electrical voltage to the electrically conductive material with a resistance such that the latter is heated under the influence of this voltage. The heat applied to the plastic causes the inside of the welding sleeve and the outside of the tube parts to be connected or to melt together. A strong, tight connection is obtained as a result.
The connecting means normally used are, for example, pins embedded in the wall of the welding sleeve, in the axial direction of the welding sleeve or perpendicularly to the axial direction of the welding sleeve whereby between two of such connecting means a desired length of electrically conductive material is present.
A disadvantage of this type is known welding sleeves resides in the fact that it is not always possible to guarantee a good electrical contact between said connecting means and the electrically conductive material as a result of which the percentage of failure in a batch of these known welding sleeves may be relatively high. Although it has indeed been attempted to overcome this drawback by welding the connecting means solidly to said electrically conductive material of the sleeve this is very troublesome and time-consuming and therefore virtually unfeasible in practice.
The object of the present invention is to provide a welding sleeve of the above mentioned type which does not have the said disadvantages and which has good electrical contact between the connecting means.
Another object of the invention is to provide a welding sleeve of this type, the connecting means being standardized in respect of positioning and shape.